The invention relates to a disc brake for a commercial vehicle having a brake caliper which straddles a brake disc and is configured as a sliding caliper, two brake pads which are arranged therein, can be moved in opposite directions and in each case have a pad carrier plate and a friction lining fastened thereon, of which an application-side friction lining can be pressed against the brake disc by way of a brake application device via at least one brake ram, and having at least one restoring device, by which the caliper can be returned after a braking-induced displacement and release of the brake.
In the functional case, that is to say in the case of a brake operation, an application of the brake pads by means of a brake application device takes place first of all by pressing of the application-side brake pad against the brake disc and subsequent pressing of the reaction-side brake pad which lies on the opposite side of the brake disc.
Whereas the application-side brake pad is pressed against the brake disc via brake rams of the brake application device, the brake caliper which is configured as a sliding caliper, is displaced counter to the pressing action of the brake application device on the application-side brake pad in order to press the reaction-side brake pad against the other side of the brake disc.
After the brake is released, the brake caliper remains in its last-mentioned position in the case of the known disc brake, in which position the brake pads, but at least the reaction-side brake pad, bear/bears, admittedly in a pressureless manner but in a grinding manner, against the brake disc. What are known as the residual wear torques which occur during driving operation as a result lead to an increased fuel consumption of the vehicle and also to a reduction of the service life both of the brake disc and of the brake pads.
A slight release of the brake pads takes place during driving operation by a wobbling of the brake disc and by way of vibrations and transverse accelerations when driving around bends. However, these effects are not sufficient to effectively prevent the grinding.
In order to avoid these disadvantages, DE 199 46 677 A1 has disclosed a disc brake having a restoring device which, after the release of the brake, returns the brake caliper into its starting position. In order, in particular, to guide the reaction-side brake pad in the non-functional position out of its contact with the brake disc, spring systems are known which are prestressed during application of the brake. After release, the brake pads are pressed back or pulled away by way of the spring energy which is stored as a result of the prestress. Here, said spring systems can be anchored in stationary components, for example, a brake carrier.
However, the restoring of the caliper is exclusively dependent on the spring travel of the restoring element, which, however, does not make possible an exact guidance back to an always identical air play dimension between the brake disc and the reaction-side brake pad. This has the result that the known disc brake represents a rather unsatisfactory solution to the problem.
This also applies when the reaction-side brake pad is attached in a positively locking manner to the brake caliper back, since, as a result of the holding forces which remain in the entire system of components which move relative to one another after release of the brake, said components have to be pressed away from the brake disc.
The invention is therefore based on the object of developing a disc brake of the generic type in such a way that a restoring of the brake caliper that remains constant in relation to the air play is ensured, and residual wear torques which occur are minimized.
This and other objects are achieved by way of a disc brake for a commercial vehicle having a brake caliper which straddles a brake disc and is configured as a sliding caliper, two brake pads which are arranged therein, can be moved in opposite directions and in each case have a pad carrier plate and a friction lining fastened thereon, of which an application-side friction lining can be pressed against the brake disc by way of a brake application device via at least one brake ram, and having at least one restoring device, by which the caliper can be returned after a braking-induced displacement and release of the brake. The restoring device is provided with a friction element which is mounted in the brake pad such that it can be displaced to a limited extent in a pressure-loaded manner in the axial direction of the brake disc. On the friction element, an elastic pressure element acts, which is held in the brake caliper and/or brake ram.
The invention is used especially in the reaction-side area of the disc brake, but can certainly also be used in the application-side area, to be precise in the reaction-side brake pad/brake ram functional unit there. In any case, a reduction in the residual wear torque is achieved by way of the invention.
According to the invention, a friction element is provided in the brake pad, to be precise in the friction lining of the brake pad, which friction element is held such that it can be displaced to a limited extent in a pressure-loaded manner in the axial direction of the brake disc. The friction element is composed of the same material as, or a more wear-resistant material than, the friction lining itself. For axial movability of the friction element in an impediment-free manner, it is mounted, for example, in a sliding sleeve which can be composed of metal or ceramic and is connected fixedly to the friction lining or the pad carrier plate.
A plunger, which is held in an axially displaceable manner in the pad carrier plate with the friction element, is provided as a further constituent part of the restoring device. The plunger is firstly connected fixedly to the friction element and is secondly in correspondence with an elastic pressure element which is held in the brake caliper and preferably consists of a compression spring in the form of disc springs, leaf springs or helical springs. However, it is also contemplated to use a pressurized cartridge as the elastic pressure element, the medium of which pressurized cartridge is compressed during brake application with the build-up of pressure and is relieved during the release of the brake application.
The pressure element can act directly on the plunger, but can also act via an intermediate element, preferably a ball which is positioned and held such that it secures the pressure element axially in the brake caliper spine and presses the plunger against the limiting means in the pad back plate. The limiting means is fixed, for example, to 0.3 mm and therefore corresponds to slightly less than half the desired air play. The friction element rubs with a slightly smaller projection beyond the friction lining; said projection is to be smaller than half of the stated theoretical air play, for example 0.3 mm.
A plurality of, in particular two, friction elements which are arranged at a spacing from one another are preferably provided, which are pressed onto the brake disc during the application of the brakes and are positioned in a planar manner with the friction lining surface, the pressure element being tensioned by way of the relative axial displacement of the friction elements and the brake caliper, including the brake pad.
During the release of the brake application, the respective friction element continues to be pressed against the brake disc via the plunger as a result of the spring force which is stored. The restoring force of the spring causes the displaceably mounted brake caliper and the displaceably mounted brake pad to be pushed away from the brake disc. The brake pad, that is to say the reaction-side brake pad here, is ideally connected to the brake caliper back in a positively locking manner.
Although a small residual wear torque with little required frictional energy is maintained, this is insignificantly small, since the friction elements bear with very small contact areas against the brake disc. An equilibrium which is free from residual wear or is approximately free therefrom is produced a short time after the braking operation. In any case, the pressing force which remains is small enough that the problems which are described with respect to the prior art no longer occur.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.